INTRODUCTION: Neural tube defects (NTD) are currently considered preventable in a significant number of cases. Strong evidence supports that pre-conceptional and early prenatal folic acid supplementation can greatly reduce the incidence of NTD. The first specific genetic abnormality to be identified in NTD was a variant in 5, 10 methylenetetrahydrofolate reductase. The presence of this variant in our population has not been studied before. The prevalence of neural tube defects in the Puerto Rican population has been established recently be the Puerto Rican Health Department to be 1.6/1000 live births which is significantly higher than in other populations. In our pilot studies, are studying the presence of the genetic variant and its association to folic acid metabolism (folate, red bleed cells folate, homocysteine, vitamin B- 12) in a group of 60 pregnant patients with a diagnosis of NTD in their fetuses and 60 pregnant controls matched by gestational age. PROPOSAL: We propose a descriptive study in a 2 years period. The purpose of this study will be to determine the prevalence of the 5,10 methylenetetrahydrofolate reductase common mutations in a group of 2,000 newborns during the neonatal screening for the most prevalent inherited conditions in Puerto Rico. The proposal was approved by the Institutional Review Board. Our long term goal is to assess the prevalence of this genetic variant and its possible role in the high incidence of neural tube defects in Puerto Rico. Due to the relation of this enzyme to folate metabolism, current folate recommendations for women in childbearing age in Puerto Rico to reduce NTD may have to be re-evaluated.